1. Field of the Invention
The present invention relates to a peel-treating agent comprising a reaction product of an aliphatic isocyanate having an aliphatic group of at least 8 carbon number with an ethylene/vinyl alcohol copolymer or polyvinyl alcohol as an effective component, and a method for producing the peel-treating agent.
2. Description of Background Art
Heretofore, there was known a urethane type peel-treating agent having an alkyl isocyanate added to an ethylene/vinyl alcohol copolymer or polyvinyl alcohol. For example, JP-B-2-7988 discloses a urethane type peel-treating agent of polyvinyl alcohol. JP-B-60-30355 discloses a urethane type peel-treating agent of ethylene/vinyl alcohol copolymer. Also, JP-B-4-28002 discloses a method for producing the urethane type peel-treating agent of ethylene/vinyl alcohol copolymer, wherein reaction including its intermediate product is carried out in a solution state by using a water-soluble solvent from the initiation to the end of the reaction.
Generally, in the production of the above peel-treating agent, an ethylene/vinyl alcohol copolymer or polyvinyl alcohol as a starting material is dispersed in an organic solvent such as toluene, and a water-soluble solvent such as dimethyl sulfoxide is added thereto with heating, and an aliphatic isocyanate such as octadecyl isocyanate is added and reacted with the ethylene/vinyl alcohol copolymer or polyvinyl alcohol. The ethylene/vinyl alcohol copolymer or polyvinyl alcohol is gradually dissolved when a water-soluble solvent such as dimethyl sulfoxide is added, and the periphery of a powder of the ethylene/vinyl alcohol copolymer or the like is reacted with an isocyanate to produce a urethane product of the aliphatic isocyanate with the ethylene/vinyl alcohol copolymer or polyvinyl alcohol (hereinafter referred to as “urethane product”). Since the urethane product is dissolved in toluene, the reaction proceeds in a solution state. In this case, in addition to an aimed urethane product, a bisurea form is by-produced and is precipitated in a reaction solution or is contained in the reaction solution, and is finally contained in the aimed urethane product. The bisurea form thus by-produced is a compound having a bond of —NH—CO—NH— in the center chained with an alkyl group of an aliphatic group at the both terminals of a molecule obtained by reaction of water and an aliphatic isocyanate used.
If the bisurea form is precipitated in the reaction solution, it damages a transportation pump when transporting the reaction solution from a reactor, and traps dusts to cause occlusion or clogging of a net (strainer), thereby lowering a productivity.
Also, if the bisurea form is contained in an aimed urethane product, the bisurea form is transferred to an adhesive agent layer to lower its adhesive force when a peel-treating agent containing the bisurea form is coated on the back side of a tape opposed to the adhesive agent.
Further, in order to obtain an aimed peel strength, an addition rate of an aliphatic isocyanate to an ethylene/vinyl alcohol copolymer or polyvinyl alcohol as starting materials is adjusted, but the isocyanate is consumed in the production of the bisurea form and a peel-treating agent having the aimed peel strength is hardly obtained. Still further, a peel-treating agent is usually supplied to a tape maker in a powdery state, but a tape maker having no facility of dissolving a peel-treating agent buys the peel-treating agent as a 10% solution and transports the solution and stores in a storing tank at normal temperature (around 25° C.). During storing at normal temperature, a bisurea form is precipitated if a temperature in the storing tank is lowered only a little by environmental temperature difference, and troubles are caused when storing or measuring an amount to be transported into a reaction tank.